[Data] Add heterogeneous Ray Data + Train release test

[scottjlee]

Why are these changes needed?

• Modifies the existing multi node train benchmark code to enable testing with heterogeneous clusters.
• Adds a new release test read_images_train_1_gpu_5_cpu with 1 GPU+5 CPU and runs on an empty model.

Results from test run of the newly added heterogeneous release test (1 GPU, 5 CPU):

cache-none = {'time': 1598.6025146509999, 'tput': 1696.9348484496704, 'extra_metrics': {}}

Related issue number

Checks

• [x] I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• [x] I've run scripts/format.sh to lint the changes in this PR.
• [ ] I've included any doc changes needed for https://docs.ray.io/en/master/.
  • [ ] I've added any new APIs to the API Reference. For example, if I added a method in Tune, I've added it in doc/source/tune/api/ under the corresponding .rst file.
• [x] I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • [ ] Unit tests
  • [x] Release tests
  • [ ] This PR is not tested :(